The present invention relates to the technical field of information exchange in client-server mode between stations connected by a communication network.
It finds general application in a method in which:
a) a network is formed by a communication hub and a plurality of stations, each associated with a coupler on the said hub,
b) at least one server-station is arranged on the network, and
c) each coupler is provided with a network communication protocol, allowing the processing of requests for consulting a resource file between certain stations known as client-stations and the server-station.
In a general way, the server allows access to the files for the clients who make the request. The server is a machine which stores in a unique and central manner a large number of files to reduce the cost of implementation (a single memory) and to simplify the administration of the files (a single area for retrieval).
There is a known communication protocol called NFS for Network File System (system of files on network), developed by the U.S. Company SUN MICROSYSTEMS, INC, in which the server offers for sharing by the clients a number of files stored according to a chosen branched chain of the files.
In this protocol, the branched chain of files is constructed by identifying in a one-to-one way each file by means of a label, also called "a file handle". This identification is made by the server. In practice, a client who wishes to access a file in the branched chain first of all requires the label of the root of the branched chain (root file handle).
The server does not keep track of distribution of the files (information and data) to the clients (stateless). In these conditions, it cannot inform the clients about modifications made to the files at the server. As a result, the clients interrogate the server regularly to verify that the data and information they have in their memory is up-to-date.
This results in important but wasteful traffic insofar as the centralised files on the server are very stable.
Further the interruption in service offered by the server for example in the case of its breakdown, directly influences the proper functioning of the clients, and with so much more severity and sharpness if, as is often the case, the centralised files are critical for the functioning of the said clients.
It should be noted that in the majority of cases, rebooting of the server secures, without any other intervention, normal recovery of the activity of the clients. Nevertheless, certain events, such as the changing on the server of a disc holding centralised files, are not transparent to the clients. In effect, the file labels depend in general on the position of the files on the central holding disc. As a result, the change of position of files at the server makes the labels already distributed to the clients wrong, and necessitates their correction.
One solution could consist of modifying the communication protocol to remedy these drawbacks. However, this would be difficult to envisage, insofar as the modifications could destroy the interoperability of the said protocol.